1. Technical Field
The present disclosure relates to a sulfur-carbon composite and a preparing method thereof, and more particularly, to a sulfur-carbon composite having an aggregated structure by performing a pressure heat treatment on a mixture of a carbonaceous conductive material and a sulfur-containing amorphous carbon material and carbonizing the same, and a preparing method thereof.
2. Description of the Related Art
Secondary batteries have been used as large capacity power storage batteries for electric vehicles or battery energy storage systems and as high performance energy sources for mobile electronic apparatuses such as mobile phones, camcorders, and laptop computers.
Lithium-ion batteries, as secondary batteries, have merits such as high energy density and large capacity per area, compared to nickel-manganese batteries or nickel-cadmium batteries. However, the lithium-ion batteries have various demerits such as deterioration of stability by overheat, low energy density, and low output properties.
To address the demerits of the lithium-ion batteries, research and development of lithium-sulfur secondary batteries or lithium-air secondary batteries having high output and high energy density is actively being performed.
Among them, the lithium-sulfur secondary battery, which uses sulfur as a cathode active material and lithium metal as an anode, exhibits an energy density of 2,500 Wh/kg, five times greater than the theoretic energy density of existing lithium-ion batteries, so that the lithium-sulfur secondary battery is suitable for batteries for electric vehicles requiring high output and high energy density.
In spite of the above merits, when sulfur is used as an active material, a use ratio of sulfur participating in an electrochemical oxidation-reduction reaction in a battery to a total amount of sulfur input as a raw material is low so that capacity of a battery is actually lower than a theoretic capacity.
Such a problem may be generated for various reasons. As a typical example, most known cathode active materials for lithium-sulfur secondary batteries are composites in which sulfur is injected into mesopores and micropores of a carbonaceous conductive material used as a support for sulfur. However, in composites according to the related art, sulfur-aggregates are generated due to irregular injection of sulfur into the composites or sulfur is not regularly distributed in the composite.
In addition, in the case of the composite in which sulfur is inserted into mesopores and micropores of a conductive material that is simply used as a support for sulfur, during electrochemical oxidation-reduction reaction of a lithium-sulfur secondary battery, the sulfur easily leaks into an electrolyte so that lifespan of the battery is deteriorated. Furthermore, as lithium-polysulfide that is a reduced sulfur leaks into the electrolyte, a shuttle phenomenon occurs in which the lithium-polysulfide moves between the cathode and the anode, or a space where sulfur in a solid phase is present is destroyed, thereby causing a negative influence on the capacity of the battery and the cycle properties.
Accordingly, there is a demand for development of a sulfur-carbon composite in which a sulfur-loading level in a sulfur-carbon composite formed of sulfur and a carbonaceous conductive material is increased and sulfur is uniformly distributed in the composite.
In addition, when the composite is used as the cathode active material of a lithium-sulfur secondary battery, it is necessary to develop a sulfur-carbon composite that may prevent sulfur in a reduced form from leaking according to the electrochemical oxidation-reduction reaction of the lithium-sulfur secondary battery.